Shielded electrical wire construction and method of manufacture

ABSTRACT

A shielded electrical wire construction, comprising an insulated wire, a conductive coating surrounding the insulated wire to provide a positive attenuation of and protection from electromagnetic and radio frequency interference. The conductive coating comprises a metallic powder dispersed in a PTFE solution. An outer insulation coating formed of PTFE surrounds the conductive coating.

FIELD OF THE INVENTION

[0001] The present invention relates to shielded electrical wire and,more particularly, to such wire having a conductive coating on the outersurface thereof which provides a positive attenuation of and protectionfrom electromagnetic and radio frequency interference.

BACKGROUND OF THE INVENTION

[0002] Up to the present time, electric wire has been provided withmetal braiding, tapes, foils or the like in order to provide a positiveattenuation of and protection from electromagnetic and radio frequencyinterference. Such shielded wire has been complicated in construction,expensive to manufacture, relatively rigid, high in weight and large indiameter.

[0003] The new and improved shielded electrical wire construction of thepresent invention is not subject to any of the disadvantages ofpreviously used shielded wire and possesses certain advantages not foundin previously used wire.

[0004] Accordingly, it is a primary object of the present invention toprovide a new and improved shielded electrical wire construction andmethod of manufacturing same wherein the shielded wire is simple inconstruction, inexpensive to manufacture, light in weight, small indiameter and of improved flexibility compared to previously usedshielded wire.

SUMMARY OF THE INVENTION

[0005] In accordance with the present invention, insulated electricalwire of any suitable type is provided with a conductive coating on theouter surface thereof in a sufficient amount to provide a positiveattenuation of and protection from electromagnetic and radio frequencyinterference. The conductive coating comprises a metallic powder ofcopper, iron, nickel, aluminum, silver, gold or carbon, alone or in anydesired mixture. The powder is blended into a dispersion coating ofpolytetrofluoroethylene (PTFE), generally known under the trademarkTEFLON, or blended into a PTFE striping ink, in a ratio that, when curedat sufficient temperature, provides a conductive surface that bonds tothe wire.

[0006] An outer insulation is applied over the conductive coating toprotect it from abrasion and chemical environments. The insulation maybe in the form of a coating of PTFE which may be in the form of a tapethat is spirally wrapped around the coated wire and then drawn through aheated metal compression sealer to provide the insulation coating aroundthe conductive coating. The outer insulation can also be in the form ofa PTFE dispersion solution or ink without any metal content.

[0007] The new and improved shielded electrical wire construction of thepresent invention is simple in construction, inexpensive to manufacture,light in weight, small in thickness and of improved flexibility comparedto previously used shielded wire utilizing metal tapes, braids, foils orthe like. Weight saving is particularly important in view of thestringent requirements for present day, lightweight space in variousenvironments, such as aeronautical environments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a is a perspective view of a portion of a shieldedelectrical wire, with parts broken away, constructed in accordance withthe principles of the present invention; and

[0009]FIG. 2 is a schematic view of apparatus for manufacturing the newand improved shielded electrical wire shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Referring to FIG. 1, the shielded electrical wire 10 of thepresent invention generally comprises an electrical wire 12 of anysuitable construction or material, an insulation coating 14 of anysuitable construction or material surrounding the wire 12, a conductivecoating 16 surrounding the insulation coating 14 and constructed inaccordance with the principles of the present invention, and an outerinsulation coating 18 surrounding the conductive coating 16 andconstructed in accordance with the principles of the present invention.The wire 12 and insulation layer 14 may be any type of conventional orsuitable PTFE insulated electrical wire. The diameter of the insulatedwire 12, 14 may be of any suitable size, e.g., approximately 0.01 to 1.1inches.

[0011] In accordance with the present invention, the conductive coating16 is applied to the outer surface of the insulated wire 12, 14 toprovide a positive attenuation of and protection from electromagneticand radio frequency interference. The conductive coating 16 comprises ametallic powder formed of copper, iron, nickel, aluminum, silver, goldor carbon, alone or in suitable mixture, which is blended into a PTFEdispersion or ink coating in a ratio that, when cured at sufficienttemperature, provides a suitable conductive surface that bonds to theinsulated wire 12, 14. As an illustrative embodiment, the metallicpowder may be blended in any suitable ratio (e.g., equal parts) with thePTFE dispersion solution or ink. Also, the metallic powder may be in aparticle size of approximately 0.1 to 10 microns.

[0012] The outer insulation coating 18 surrounds the conductive coating16 and may be formed by spirally wrapping a PTFE film tape around thecoated and insulated wire, and then heating and compressing it toprovide the outer insulation coating 18. Alternatively, the outerinsulation coating 18 may be formed by drawing the wire with theconductive coating 16 thereon through a PTFE dispersion solution or inkreservoir with no metallic content.

[0013]FIG. 2 illustrates one embodiment of apparatus 20 formanufacturing the shielded electrical wire 10 shown in FIG. 1 inaccordance with the method of present invention. The blended metallicpowder-PTFE dispersion solution or ink is provided in a reservoir 22that may be agitated or rotated by a drive motor 24 or any othersuitable device. Preferably, the metallic powder is mixed in varioussuitable ratios with the PTFE dispersion solution or ink and the mixtureis set for at least one hour to allow any air to escape. The mixture isthen gently re-mixed prior to placement in the reservoir 22.

[0014] Before the insulated wire 12, 14 is coated, it is cleaned in anysuitable manner, such as by wiping with a paper towel saturated withmethyl ethyl keytone (MEK) and allowed to dry. The insulated wire 12, 14is then preheated to approximately 250° F. and passed through themetallic powder-PTFE dispersion solution in the reservoir 22 so as to becoated thereby. The insulated wire 12, 14 is passed through thereservoir at a rate of approximately one-half inch per second.

[0015] After the coated wire 12, 14, 16 exits the reservoir 22, it isheated to approximately 800° F. to cure the conductive coating 16thereon. This can be accomplished in any suitable manner, such as bypassing the coated wire through a hot air field. The conductive coating16 may have a thickness of approximately 0.0005 to 0.005 microns.

[0016] The cured, coated wire 12, 14, 16 is then preheated toapproximately 650° F. and, in one embodiment, a PTFE film wrap 26 isspirally wound thereon to form the outer insulation coating 18. Thespirally wrapped wire is then passed through a metal compression sealer28 of any suitable construction wherein it is heated to approximately800° F. to form and cure the outer insulation coating 18 on theconductive coating 16. It is also possible to form the outer insulationcoating 18 by passing or drawing the cured, coated wire 12, 14, 16through a heated PTFE dispersion solution or ink in a reservoir with nometallic content. The outer insulation coating may have a thickness ofapproximately 0.003 to 0.006 microns.

[0017] It will be readily seen from the foregoing description that thenew and improved shielded electrical wire 10 of the present invention issimple in construction, easy and inexpensive to manufacture, light inweight, small in diameter and of improved flexibility compared to thepreviously used metal shielded wire utilizing tapes, braids, foils orthe like.

[0018] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-6. (Canceled)
 7. A method of manufacturing an electrical wire that isshielded from electromagnetic and radio frequency interference,comprising: passing insulated wire through a reservoir containingmetallic powder dispersed in a PTFE solution to provide a conductivecoating on the wire; heating the coated wire to cure the conductivecoating thereon; and applying an outer PTFE insulation coating aroundsaid conductive coating.
 8. The method of claim 7 wherein the wire isPTFE insulated.
 9. The method of claim 7 wherein the insulated wire iscleaned and preheated before passing it through said reservoir.
 10. Themethod of claim 9 wherein the insulated wire is preheated to atemperature of approximately 250° F.
 11. The method of claim 7 whereinthe coated insulated wire is heated to approximately 800° F. to cure theconductive coating thereon.
 12. The method of claim 7 wherein the PTFEsolution containing the metallic powder is agitated as said insulatedwire is passed therethrough.
 13. The method of claim 7 wherein the outerPTFE insulation coating is formed by spirally wrapping a PTFE filmaround the coated insulated wire, and thereafter heating and curing thewound PTFE film to cure and seal the outer insulation coating around theconductive coating.
 14. The method of claim 13 wherein the PTFE filmwound around the coated insulated wire is cured by passing it through aheated metal compression sealer at a temperature of approximately 800°F.
 15. The method of claim 13 wherein the coated insulated wire ispreheated to approximately 650° F. before the PTFE film is spirallywound thereon.
 16. The method of claim 7 wherein the insulated wire ispassed through the reservoir at a rate of approximately one-half inchper second.